Various physical properties of fluids such as the concentration of various fluids, for example most acids, vary as a function of density of the fluid. Since many devices are in use for measuring the density of materials, such as shown in my U.S. Pat. Nos. 3,145,559; 3,177,705; and 3,449,940, the density of a fluid may be readily measured to provide a measurement of the property of the fluid which varies directly with the density. However, the properties of some materials, such as the concentration of sulfuric acid, is a curve which both increases and decreases relative to the density of the sulfuric acid and therefore a measurement of density would not give a valid indication of the concentration of sulfuric acid. Furthermore, various properties of materials that do vary with the density of the material are affected by environmental conditions such as temperature, the presence of other fluids, corrosion, and material buildup which affect density measurements and therefore would prevent accurate density measurement.
The present invention is directed to a method and apparatus for measuring a physical property of a material that varies nonlinearly relative to the density of the fluid in which the density of the fluid is measured for determining the value of the property being measured. In addition, the present method and apparatus overcomes errors caused by environmental conditions such as temperature changes, material buildup on the density measuring apparatus, corrosion, and the presence of other materials present in the fluid.